1. Field of the Invention
The present invention relates to a manufacturing apparatus of a torsion beam of a suspension apparatus, and more particularly, to a hybrid method manufacturing apparatus for a torsion beam which can improve dimensional accuracy by high-temperature molding and in which additional heat treatment such as tempering is selectively performed only when it is necessary to increase toughness because only a martensite structure is not formed in quenching treatment.
2. Description of the Related Art
In general, concentration of a vehicle's load and inclination of a vehicle which are generated by turning the vehicle are adjusted by roll control and for the purpose of the roll control, a torsion bar or a torsion beam is applied to a suspension apparatus.
Both ends of the torsion bar or the torsion beam are twisted to control roll when a wheel center phase difference between both wheels occurs due to turning. Therefore, the torsion bar or the torsion beam should have torsional rigidity.
The torsional rigidity is easily applied to the torsion bar, while an additional reinforcing member should be attached over both ends of the torsion beam in order to apply the torsional rigidity to the torsion beam.
Therefore, it is very important to adopt a molding method of applying excellent torsional rigidity to the torsion beam itself in the case of the torsion beam. For example, a heat treatment process such as tempering or quenching is being performed in order to increase tensile strength and improve rigidity at a molding process of the torsion beam.
The heat treatment method is divided into an indirect cooling method in which a product is heated thereafter, cooled and molded in a mold and a direct cooling method in which a product is molded at room temperature and thereafter, heated and quickly cooled with water.
A tubular coupled torsion beam axle (CTBA) generally adopted in a rear suspension apparatus of a medium-sized passenger car requires tensile strength of approximately 140 kg/mm2.
Since the tensile strength of the tubular CTBA to which the indirect cooling method is applied is in the range of 100 kg/mm2 to 140 kg/mm2, reliability is not high, while since the tensile strength of the tubular CTBA to which the direct cooling method is applied is 140 kg/mm2, the reliability is high.
In general, since the quenching treatment used in the direct cooling method is a method in which a material is heated at high temperature and thereafter, the heated material is quickly cooled with water for a short time, a possibility that a cross section of the material will be changed due to quick cooling is high and a risk that even the manufactured product will not meet a designed standard increases.
Therefore, in the direct cooling method, an additional jig capable of preventing the change of the cross section of the material caused by heat treatment should be used, which is inconvenient for a user.
Further, since an internal structure quickly cooled in the quenching treatment is transformed to the martensite structure which is vulnerable to a fatigue crack, another heat treatment process such as tempering for applying toughness after the quenching treatment needs to be additionally performed. As a result, these dual treatments cannot be help causing an increase in the number of processes, a decrease of productivity, and an increase of manufacturing cost.